Conventionally, semiconductor processing techniques such as lithography, vacuum evaporation, and etching have been used for the fabrication of transistors which drive or control display apparatuses such as liquid crystal displays and organic electro-luminescence displays. However, in view of desires for display apparatuses having an increased area, a problem exists in that use of such conventional processing techniques requires tremendous production equipment and increases the production cost. As a means for solving such problems, transistor production methods which utilize printing technique are drawing attention, in the place of conventional semiconductor processing techniques such as lithography, vacuum evaporation, and etching. Moreover, by using a flexible substrate such as plastic instead of the glass substrate which has mainly been used in the conventional techniques, it becomes possible to realize features such as thinness, light-weightness, and flexibility over conventional products. Therefore, methods of producing transistors on a flexible substrate are drawing attention.
As materials of conventional transistors for driving or controlling display devices, amorphous silicon and polysilicon have mainly been used. However, in current technology, these materials are subjected to film formation via vacuum processes such as a vapor phase deposition method and an evaporation method, and cannot be adapted to printing processes. Moreover, since a relatively high process temperature is required, there are constraints on the substrate material. For example, low-melting point materials, e.g., a plastic substrate, cannot be used.
As a means for solving these problems, a method has been proposed that disperses very small-sized single crystals of silicon in a solution to produce a “silicon ink”, which is then applied on a substrate, thus fabricating a transistor composed of silicon crystals through a printing process. Non-Patent Document 1 discloses formation of a transistor through a printing process that uses silicon nanowires which are fabricated by a VLS growth technique as a material. Non-Patent Document 2 discloses formation of a transistor through a printing process which uses thin pieces of silicon that have been cut out from an SOI substrate as a material. By using these techniques, not only 1) low costs are realized based on a printing process, but also there are advantages in that 2) higher mobility and less variation than those of conventional amorphous silicon and polysilicon are realized because single crystals of silicon are used, and that 3) there is a much greater freedom of substrate material selection because silicon film formation near room temperature is enabled. Therefore, by using these techniques, it becomes possible to fabricate a high-performance transistor of single-crystalline silicon on a plastic substrate, for example, whereby novel devices that were not conventionally available can be realized, e.g., flexible displays.
[Non-Patent Document 1] “High-performance thin-film transistors using semiconductor nanowires and nanoribbons”, Nature, vol. 425, 18 Sep. 2003, pp. 274-278.
[Non-Patent Document 2] “A printable form of silicon for high performance thin film transistors on plastic substrates”, Applied Physics Letters, vol. 84, 28 Jun. 2004, pp. 5398-5400.